A piston ring for an automobile engine has been proposed, which has remarkably good low-friction property and can improve fuel-efficiency more than conventional combinations of an iron material and an organic molybdenum compound (see Patent Document 1).
The piston ring for an automobile engine is used for automobile engines that include a sliding member sliding in the presence of lubricating oil. The sliding surface of the sliding member is coated with a hard carbon film that contains hydrogen atoms in an amount of 25 at % or less. In the piston ring for an automobile engine, the hard carbon film has improved adhesion and improved durability, which are obtained by a pretreatment of chromium plating on the sliding surface of the sliding member prior to the hard carbon film coating.